Semisubmersible floating sea platform



April 2l, 1970 J. w|PK|NK ET AL i 3,507,239

SEMISUBMERSIBLE FLOATING SEA PLATFORM Filed July 1. 196s 3 sheets-sheet 1 E g'- l fr' f April 2l, 1970 J.w|PK|NK ETAL i 3,507,239

SEMISUBMERSIBLE FLOATING SEA PLATFORM Filed July l, 1968 5 Sheets-Sheet 2 April 2l, 1970 J. wlPKlNK ETAL 3,507,239

SEMISUBMERSIBLE FLOATING SEA PLATFORM Filed July 1. 1968 A 3 Sheets-Sheet 3 United States Patent O U.S. Cl. 114-.5 11 Claims ABSTRACT OF THE DISCLOSURE A floating sea platform including a horizontal deck mounted on vertical columns provided with float members at their lower ends, and having a plurality of bracing members extending from the upper and lower ends of each column to a common joint located in the plane including the bottoms of the columns.

BACKGROUND OF THE INVENTION This invention is concerned with a floating platform for the open sea comprising a number of vertical columns carried by floaters at their lower ends, the floaters having a larger horizontal cross-sectional area than the columns, which columns carry a horizontal work-deck and are kept in relative position by means of at least a number of horizontal and/or inclined bracings between adjacent columns.

A floating platform is known in which a relatively stiff deck structure is supported by three columns located substantially at the corners of an equilateral triangle, the columns being carried by shoe shaped oaters. Dependent upon the local conditions, work with this floating platform is done in a ballasted condition in which the floaters are sunk to a substantial depth below water surface, but the deck structure lies at a height above the maximum wave tops. In order to be towed from one location to another, ballast is disposed of until the oaters emerge above water surface. The structure is stiffened by providing a kind of trussing in the faces between the columns, but it has appeared in practice that structural requirements should be more stringent as to its form stability, a vulnerable point in, for instance, a collision.

SUMMARY OF THE INVENTION In accordance with this invention a joint of bracings is located between the columns, and bracings emanate from this joint to upper and lower points of the columns. Thereby, a spatial structure is obtained which is plurally statically undetermined, so that certain bracings may give way without endangering the form stability of the structure. Also, from a point of view of utility considerations, a bracing or a number of bracings may be left out without sacrificingthe stability of the structure. In an arrangement in which the columns are located at the corners of an equilateral triangle the interconnections between the columns at a lower level are maintained, but the stiifering of the faces between the columns may be left out.

In accordance with the invention, the central joint may be connected to a second joint located centrally in the deck structure, deck girders emanating from this second joint to the columns. Thereby, the deck structure can be designed less stiff and lighter.

Preferably, the joint and the connections of this joint with the lower points of the columns are located in a In order to improve the safety, according to the invention, the platform may be provided with live columns located substantially at the corners of a regular pentagon. With ve columns, a leak in one of the columns or oaters can be compensated by ballasing two columns and/or floaters located at the other side of the platform. In addition, such a platform can easily be made selfdocking, as contrary to a platform on three floaters.

Also, statically, the structure on five floaters offers particular advantages. It can be generally proved that a stmcture in which the columns are located at the corner points of an n-sided polygon having 2714-2 joints in all, need 6n bars to make the structure statically determined. However, in the present structure there are 7n+l bars (including columns and bracings). Therefrom, it appears, that ri-f-l bracings may be left out to still keep the structure statically determined. Thus, six bracings may be left out in a platform on five floaters which provides a large margin of safety, even if a few bracings would be left out because of utility considerations.

Preferably, in accordance with the invention the bracings are left out between two adjacent columns in a fivecolumn oating platform, so that an entirely open face results on one side. Thereby a vertically free face is made above which a drilling rig can be located, so that the platform can be located freely over the well.

Since the platform is towed in unballasted condition, the oaters suffer from the slamming of the waves both above and below the surface. According to the invention the influence of this slamming is appreciably lessened, in that the' transition of each column to its corresponding floater is conically shaped, as is the bottom of each floater. The particular importance thereof is that towing at a certain speed is much easier under poor weather conditions as compared with conventionally designed oaters having a at top and bottom.

In a structure as the present one it is of vital importance that the joints, in particular the central joint, should be designed and constructed in accordance with high standards, in which material stresses in the bracings are transmitted to the other bracings without high local stress concentrations.

To that effect, according to the invention, the joints are designed so that they are composed of a core in the shape of a polyhedron having a number of faces corresponding to at least the number of bracings leading to the joint, each bracing being connected to a face of the core through a transition piece composed, on the one side, of flat faces interconnecting a straight line of the core to a point of the circumference of the bracing, and, on the other side, of faces each interconnecting a circumferential portion of the bracing between two adjacent points interconnected to a line of the core and a point of intersection of two lines interconnected to a point of the bracing, whereby a continuous closed surface is obtained. A bracing having a polygonal cross-section can always be connected to a cross-section of different polygonal shape by means of flat faces. A connection of a rod having an n-sided polygonal cross-section to an m-sided polygonal cross-section requires n-i-m triangular planes to obtain a completely closed surface of the transition piece. In order to connect a circular to a polygonal cross-section the number of at faces corresponds with the number of sides of the polygon, this number being increased by the same number of pieces of inclined conical shape to complete the transition piece. Of course, the length of the transition piece has to be chosen sufficiently long to ensure a uniform distribution of the stresses.

In the case of a platform in which the cross-section of the bracings is circular and a vertical central bracing is joined to five pairs of bracings located in vertical planes which connect the joint Vto higher and lower points of the columns, respectively, the core may, according to the invention, advantageously have the shape of a vertical prism having a regular live-sided cross-section.

According to the invention, the core may be composed of at plates which keeps its construction simple.

Also, according to the invention, the core may be provided with stiifening plates provided with or without recesses to provide a greater stiffness to the core. If the angle between an incoming bracing and the faces which have to take up the stresses becomes too large, diagonal planes are advantageous to secure a best possible transmission of the stresses.

Another possible feature of the platform according to the invention is that the iloaters extend entirely freely down the columns. The iloaters can be designed for optimum dynamic characteristics which, however, are dependent upon local conditions, such as wave length and wave height. So, if a platform is to be moved to an area of different prevailing conditions, the oaters can advantageously be cut olf and replaced by differently shaped oaters of the same volume adapted to the said different prevailing conditions without touching the characteristics of the main structure.

BRIEF DESCRIPTION OF THE DRAWINGS In the appended drawing a preferred embodiment of the invention is shown of a platform and a joint to further illustrate the invention.

FIGURE 1 shows a side view of the oating platform.

FIGURE 2 shows atop view of this platform, the workdeck and corresponding girders being left out.

FIGURE 3 shows a sketch of the center lines of the bracings forming the spatial trussing in perspective.

FIGURE 4 shows a side view of a joint according to the invention.

FIGURE 5 shows a top view of a transition piece between bars of three-and live-side cross-sections respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT The floating platform derives its floating ability substantially from the floaters 1 of circular cross-section connected to the columns 3 through a conical transition 2. The lower side of the floaters 1 has the shape of a truncated cone 4.

On top of the columns 3 is mounted a deck-structure 5, which may be composed of a single deck or a number of decks. Preferably, the number of decks is three for a floating drilling platform to provide room for crew accommodation, storage spaces for material and spaces for machinery and the like.

In the deck structure lie deck edge girders 6 and radial girders 7, as shown in FIGURE 3.

A joint 8 is provided in a lower horizontal plane, which lies above the water surface in the condition of the platform to be towed. From this joint 8 bracings 9 radiate in a horizontal plane, spatial bracngs 10 radiate to the upper ends of the columns, and a vertical bracing 11 extends upward to the deck structure.

Furthermore, circumferential bracings 12 are provided in the horizontal plane at the level of joint 8. One diagonal bracing 13 is mounted in each side face between the columns.

As shown in FIGURES 2 and 3, all bracngs between two columns are left out in one vertical face of the structure, so that a wedge shaped opening results at that location. A drilling rig is mounted above this opening which, thus, can be brought freely over a well of which the casing may extend above Water.

Including the ve stabilization columns the presently proposed structure has 33 bars, whereas 30 bars are needed for a statically determined structure. These additional three bars may for instance be left out of the diagonal bracings in the side faces of the spatial frame- CII work and, thus, constitute a safety margin for the structure.

The location of joint 8 does not coincide with the center of the circumscribed circle of the regular pentagon according to which the columns are located. The location of joint 8 is shifted to the side of the drilling rig location for a more favorable load distribution by the heavy, oneside load of the drilling rig.

As seen in FIGURE 3, the joint of the radial girders 7 in the upper face is located vertically above joint 8, but this is not necessary for the reliability of the structure.

FIGURE 4 shows joint 8 in detail. This joint has a central portion or core 14 in the shape of a vertically positioned prism of pentagonal cross-section of which the angles between the sides may be adapted to the angles under which the bracings meet. In horizontal projections, these angles are each others supplements. A regular pentagonal cross-section will fully suffice if the deviations are not too large.

The bracings leading to the joint are of circular crosssection and the connection between bracing 11 and core 14 is formed by a transition piece composed of at faces 15 and part-conical faces 16. Thereby, an advantageous transmission is ensured of the stresses in rod 11 to the faces of core 14.

In connecting a spatial bracing 10 to a vertical side face of core 14, firstly, bracing 10 is connected to a bar 17 of a square cross-section through a previously described transition piece, the bar 17 being welded to the corresponding face of core 14.

As seen in the drawings, the number of at faces 1S of the transition piece equals the number of sides of the prism and in between lie an equal number of part-conical faces.

FIGURE 5 shows by way of example, how a triangular bar can be connected to a pentagonal figure. The number of fiat faces required equals the sum of the number of sides of both areas to be connected, in the present case, 3-1-5=8.

When forming a joint according to the invention, the center lines of the bracings meet at and pass through a common point of intersection to maximize the strength of the joint and provide for uniform stress distribution.

It will be apparent that the application of such a joint is not limited to an application in floating sea platforms,

but may be useful in other support structures in general.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departingl from the spirit and scope of the invention.

What is claimed is:

1. A floating platform for the open sea including a number of vertical columns carried by iloaters at their lower ends, the oaters having a larger horizontal cross-sectional area than the columns, a horizontal work-deck carried by the columns, and a plurality of horizontal and inclined bracing members between adjacent columns to maintain the relative position of the columns, comprising:

(a) a single bracing member joint centrally located between all ofthe columns, and

(b) a plurality of bracing members emanating from the single joint to upper and lower points on the columns.

2. A oating platform according to claim 1 further comprising a bracing member connecting the joint to a second joint of deck girders emanating to the columns and located in the deck structure.

3. A floating platform according to claim 1 in which the joint and the bracing members between the joint and the lower points on the columns lie in one flat plane.

4. A floating platform according to claim 1 in which the platform has five columns disposed according to the corners of a regular pentagon.

5. A oating platform according to claim 4 in which the bracing members between two adjacent columns of the ve are left out, resulting in an entirely open face at one side.

6. A oating platform according to claim 1 in which the transition of each column to a floater is frusto-conical andthe bottom of each oater is frusto-conical.

7. A floating platform according to claim 1 in which the joint comprises:

(a) a core of polyhedral shape having a number of faces corresponding to at least the number of bracing members leading to the joint, and

(b) a plurality of transition pieces connecting each bracing member to a face of the core, each transition piece comprising a plurality of flat faces interconnecting a straight line on the core to a point of the circumference of the bracing member alternating with a plurality of faces interconnecting a circumferential portion of the bracing member between two adjacent points connected to a line of the core, to a point of intersection of two lines connected to a point of the bracing member, so that a continuous closed surface is obtained.

8. A floating platform according to claim 7 in which the bracing members are of circular cross-section and a vertical central bracing member joins ve pairs of bracing members located in vertical planes and connecting the joint to higher and lower points, respectively, on the columns, characterized in that the core has the shape of a vertical prism of regular pentagonal cross-section.

9. A floating platform according to claim 7 in which the core is comprised of flat plates.

10. A oating platform according to claim 8 in which the core is provided with stitfening plates to attribute a greater stiffness to the core.

11. A oating platform according to claim 1 in which the oaters extend entirely freely down the columns.

References Cited UNITED STATES PATENTS 3,154,039 10/1964 Knapp. 3,294,051 12/1966 Khelstousky. 3,397,545 8/1968 Leavitt. 3,443,543 5/1969 Wiumet a1.

TRYGVE M. BLIX, Primary Examiner U,S. Cl. X.R. 61-46.5 

